During the early 1950s, Moore worked as a male model, appearing in print advertisements for as wide a range of products as toothpaste and knitwear, something which many critics have used as typifying his lightweight credentials as an actor. His earliest known television appearance, at a time when the BBC were the only channel, was on May 27 1950, in Drawing Room Detective, a one-off programme. Presented by veteran BBC announcer Leslie Mitchell, it invited viewers at home to spot clues to a crime during a playlet, whose actors included Alec Ross (first husband of Sheila Hancock), Michael Ripper, and Moore. Barring interviews, he has not worked for BBC television since.

Although Moore won a contract with MGM in the 1950s, the films which followed were not a success and, in his own words, "At MGM, RGM (Roger George Moore) was NBG no bloody good". His starring role in The Miracle, a version of the play Das Mirakel for Warner Bros., had been turned down by Dirk Bogarde. Eventually, it was television which made his name. He was the eponymous hero in the serial Ivanhoe, a very loose adaptation of Sir Walter Scott's romantic novel, and he also appeared in the series The Alaskans. He also played an English cousin of James Garner as television's Maverick, the Wild West gambler.

It was not until 1961 that worldwide fame arrived, when Lew Grade cast him as Simon Templar in a new adaptation of The Saint novels by Leslie Charteris. The television series was made in the UK with an eye on the American market, and its success there (and in other countries) made Moore a household name. It also established his suave, quipping style which he would carry forward to James Bond. Moore would also go on to direct several episodes of the later series, which moved into colour in 1967. The opinion has often been expressed that the monochrome episodes of the series, which were closer adaptations of Charteris' work, were superior to the colour episodes, which displayed a stronger leaning towards fantasy and were arguably trying too hard to imitate other shows of that time.

The Saint ran for seven years and 118 episodes, making it (with The Avengers) the longest-running series of its kind on British television. Moore however grew increasingly tired of the role, and was keen to branch out. He made two films immediately after The Saint ended: Crossplot, a lightweight "spy caper" movie, and the more challenging The Man Who Haunted Himself (1971). Directed by Basil Dearden, it gave Moore the opportunity to demonstrate a wider versatility than the role of Simon Templar had allowed, although the reviews at the time were lukewarm and it did little business at the box office.

Television lured him back however, to star in what has become another "cult" series, The Persuaders!, alongside Tony Curtis. Even more lightweight in tone than The Saint, it featured the adventures of two millionaire playboys across Europe. It was for this series that Moore was paid the then unheard-of sum of one million pounds for a single series, making him the highest paid television actor in the world. However as Lew Grade admitted in his autobiography Still Dancing, Moore and Curtis "didn't hit it off all that well", Curtis refusing to spend more time on set than was strictly necessary, while Moore was always willing to work overtime. The series failed in America, where it had been pre-sold to ABC, and an article in TV Zone magazine has alleged that, on its premiere in Britain on the ITV network, it was beaten in the ratings by repeats of Monty Python's Flying Circus on BBC1. When Channel 4 repeated both The Avengers and The Persuaders! in 1995, it was generally agreed that the latter, which had not been seen for many years, had not aged as well as the former, and it has not been on terrestrial television since.

Since then, The Persuaders has enjoyed something of a renaissance both on television and DVD, with the "rivals" Moore and Curtis reuniting to provide commentaries on the most recent issues. In France, where the series (entitled Amicalement Vôtre) had always been popular, the DVD releases accompanied a monthly magazine of the same name.